Clinical Biomechanics - Articles in Press

On stabilization of loosened hip stems via cement injection into osteolytic cavities - Corrected Proof

A. Andreykiv, D. Janssen, R.G.H.H. Nelissen, E.R. Valstar — 2012-05-14

Abstract: Background: Cement injection into osteolytic areas around the cement mantle is a technique for refixation of loose hip implants for patients who cannot undergo standard revision surgery. Preliminary clinical results show the improvement in walking distance, patients' independence and pain relief.Methods: In this study, we use a detailed finite element model to analyze whether cement injection into osteolytic areas contributes to the overall implant stability. We study the effect of various factors, like location and size of osteolytic areas, interface conditions and bone stiffness on bone–cement relative motion.Findings: Presented results demonstrate that the procedure is most effective for the osteolytic areas located in the proximal region of the femur, while factors like a thin layer of residual fibrous tissue around the injected cement, that was not removed during the surgery, combined with reduced bone stiffness reduce the efficiency of the procedure.Interpretation: Cement injection is able to stabilize loosened hip prostheses. However, it is important to remove the fibrous tissue layer completely, as even a thin layer will negatively influence stabilization. We will focus our research efforts on developing fibrous tissue removal techniques in order to optimize this minimally invasive treatment.

Biomechanical modeling of open locks of the human temporomandibular joint - Corrected Proof

Matthijs Tuijt, Jan Harm Koolstra, Frank Lobbezoo, Machiel Naeije — 2012-05-14

Abstract: Background: Patients with hypermobility of the temporomandibular joint may have problems closing their mouth after opening widely. In the worst case, the mandibular condyles become trapped in front of the articular eminences and the jaw muscles cannot reposition them into the fossae (open lock). The difference in ease of closing the jaw between patients and non-patients is presently not well understood.Methods: Wide opening and subsequent jaw closing were simulated with a biomechanical model in a forward dynamics approach. The effect of anterior slope angle and orientation of jaw-closing muscles on condylar travel was determined.Findings: The mandibular condyles traveled anterior of the eminences and back into the fossae uneventfully with backwardly oriented jaw closers and eminences with a gentle anterior slope. However, combinations of relatively forward oriented jaw closers and a steep anterior slope caused the condyles to continue traveling anteriorly upon jaw-closing attempts, ending in an open lock position.Interpretation: Our results indicate that for the masticatory system to reach an open lock, various unfavorable combinations of jaw-closer orientation and anterior slope angle exist within normal physiological ranges. These findings could be relevant for maxillofacial surgeons, both for the diagnostic process and for clinical decisions, regarding patients suffering from open locks.

Kinematic evaluation of patients with total and reverse shoulder arthroplasty during rehabilitation exercises with different loads - Corrected Proof

2012-05-14

Abstract: Background: Following shoulder arthroplasty, any well-planned rehabilitation program should include muscle strengthening. However, it is not always clear how different external loads influence shoulder kinematics in patients with shoulder prostheses. The objective of this study was to describe shoulder kinematics and determine the contribution of the scapulothoracic joint to total shoulder motion of patients with total and reverse shoulder arthroplasties and of healthy individuals during rehabilitation exercises (anteflexion and elevation in the scapular plane) using different loading conditions (without external load, 1kg and elastic resistance).Methods: Shoulder motions were measured using an electromagnetic tracking device. A force transducer was used to record force signals during loaded conditions using elastic resistance. Statistical comparisons were made using a three-way repeated-measures analysis of variance with a Bonferroni post hoc testing.Findings: The scapula contributed more to movement of the arm in subjects with prostheses compared to healthy subjects. The same applies for loaded conditions (1kg and elastic resistance) relative to unloaded tasks. For scapular internal rotation, upward rotation and posterior tilt no significant differences among groups were found during both exercises. Glenohumeral elevation angles during anteflexion were significantly higher in the total shoulder arthroplasty group compared to the reverse shoulder arthroplasty group.Interpretation: Differences in contribution of the scapula to total shoulder motion between patients with different types of arthroplasties were not significant. However, compared to healthy subjects, they were. Furthermore, scapular kinematics of patients with shoulder arthroplasty was influenced by implementation of external loads, but not by the type of load.

Shear strength of the human lumbar spine - Corrected Proof

2012-05-11

Abstract: Background: Shear loading is recognised as a risk factor for lower back pain. Previous studies of shear loading have either not addressed the influence of age, bone mineral density, axial height loss due to creep or were performed on animal specimens.Methods: Intact human lumbar motion segments (L2–3) were tested in shear using a modified materials testing machine, while immersed in a Ringer bath at 37°C. Vertebrae were rigidly embedded in neutral posture (0° flexion) and subjected to a constant axial compression load of 500N. Shear was applied to three groups: ‘Young-No-Creep’ (20–42years), ‘Young-Creep’ (22–38years, creep 1000N for 1h) and ‘Old-No-Creep’ (44–64years). Failure was induced by up to 15mm of anterior shear displacement at a rate of 0.5mm/s. The trabecular and apophyseal joint bone mineral densities were evaluated from computed tomography images of the intact lumbar spines.Findings: Peak shear force correlated positively with trabecular bone mineral density for specimens tested without axial creep. No significant differences were observed with respect to age. During shear overload specimens increased in height in the axial direction.Interpretation: Trabecular bone mineral density can be used to predict the peak force of lumbar spine in shear in neutral posture.

Evaluation of the constitutive properties of native, tissue engineered, and degenerated articular cartilage - Corrected Proof

A. Seifzadeh, D.C.D. Oguamanam, M. Papini — 2012-05-11

Abstract: Background: Conventional models to evaluate degenerated cartilage do not consider nonlinear permeability and proteoglycan viscous effects. Some models also utilize spring elements to represent the viscous effects of the fibers, thus application tothe modeling of nonuniform deformations such as those that occur in indentation tests. The purpose of this study was to assess the changes in the mechanical behavior of tissue engineered and degraded cartilage while addressing these shortcomings and limitations.Methods: An inverse finite element method was used to determine the material properties of native and tissue engineered cartilage from indentation test data. The engineered cartilage was evaluated 3 and 9months after implantation into osteochondral defects in the trochlear groove of sheep stifles. The strain rate dependent responses of the engineered and native cartilage in unconfined compression were also determined for strain rates ranging from 0 to 20%s−1. The material properties of bovine cartilage before and after proteoglycan depletion and collagen degradation were also compared using unconfined compression test data from the literature.Findings: For a given strain, the stiffness of the engineered cartilage was approximately one tenth of that of the native cartilage both at 3 and 9months. The model appeared to be able to predict the equilibrium and transient mechanical function of degenerated cartilage, and discerned the proteoglycan loss from collagen degradation.Interpretation: The model can be used for high strain and dynamic analysis of cartilage, and may in the future allow the determination of the load bearing capability of engineered cartilage.

Spinal loads during position changes - Corrected Proof

A. Rohlmann, R. Petersen, V. Schwachmeyer, F. Graichen, G. Bergmann — 2012-05-10

Abstract: Background: Recommendations exist how patients should change from one body position to another in order to keep the spinal loads low. However, until now it is not clear whether the loads are in fact lower if the patients follow these recommendations. The aim was to measure the loads while changing the body position.Methods: Telemeterized vertebral body replacements have been inserted into 5 patients who had a severe compression fracture of a lumbar vertebral body. The acting loads were measured during a changing of the body position while lying and when moving from lying to sitting, from sitting to standing and vice versa.Findings: When the lying patients changed their position according to the physiotherapist's recommendations, the resultant force was nearly as high as it was during relaxed standing. Otherwise, the force was nearly twice as high. Changing from a lateral lying position to sitting and vice versa caused forces of about 180% of those seen for standing when the recommendations were heeded. Without instructions, the loads were about 70% higher. Use of a trapeze bar mounted to the bed did not increase the loads. Rising from a chair with the arms hanging down laterally led to average resultant forces of 380% related to standing. Placing the hands on armrests reduced this value to 180%.Interpretation: High forces may act on the spine when changing from one body position to another. These loads can be minimized when following the physiotherapist's instructions and when supporting the upper body by the arms.

The role of the scapulo-thoracic and gleno-humeral joints in upper-limb motion in children with hemiplegic cerebral palsy - Corrected Proof

Sylvain Brochard, Mathieu Lempereur, Linda Mao, Olivier Rémy-Néris — 2012-05-04

Abstract: Background: The pathophysiology of abnormal shoulder motion in children with hemiplegic cerebral palsy is not yet well understood. The aim of this study was to compare the motion of the two principle shoulder joints in children with hemiplegic cerebral palsy and typically developing children.Methods: 10 children in each group carried out 6 tasks recorded by an optoelectronic system. The analysis protocol was based on an acromion marker cluster, a functional method to determine the gleno-humeral rotation center and different Euler sequences thus providing three dimensional thoraco-humeral, scapulo-thoracic and gleno-humeral kinematics during upper-limb motion.Findings: In the children with hemiplegic cerebral palsy, the scapulo-thoracic joint was more protracted (P<0.05) and tended to be more laterally rotated depending on the tasks and the degree of humeral elevation. The gleno-humeral joint was limited in elevation (P<0.09), internal rotation (P<0.05) and plane of elevation (P<0.05) depending on the task. At rest, the orientation of the arm was more related to the scapular posture than to the gleno-humeral orientation, the latter which appeared to compensate the initial internal arm rotation at the beginning of the motion.Interpretation: The scapulo-thoracic joint plays a key role in arm posture at rest and during motion but does not seem to limit arm motion. The gleno-humeral joint compensates the scapula orientation at small degrees of humeral elevation but has a reduced total range of motion. Clinical management should focus on both joints taking into account their respective roles in upper-limb motion in this population.

Corrigendum to ‘The effect of lateral epicondylosis on upper limb mechanical parameters’ [Clinical Biomechanics 27 (2012) 124–130] - Corrected Proof

2012-04-30

The authors regret that in Section 2.4 Measurement of pain-free grip strength on page 126, it is mentioned that “The grip span of the dynamometer was set at 4in.”. The sentence should read, “The grip span of the dynamometer was set at 2in.”.

Are conventional reconstruction plates equivalent to precontoured locking plates for distal humerus fracture fixation? A biomechanics cadaver study - Corrected Proof

Ryan C. Koonce, Todd H. Baldini, Steven J. Morgan — 2012-04-27

Abstract: Background: The optimal plate type and configuration for distal humerus fracture fixation has yet to be defined. Available biomechanical studies show conflicting results. No existing studies compare conventional reconstruction plates to newer precontoured distal humerus locking plates in both parallel and perpendicular configurations.Methods: Three groups of humerus specimens were compared via biomechanical testing in a cadaver model simulating metaphyseal comminution. Group 1 consisted of conventional reconstruction plates in a perpendicular configuration. Group 2 used precontoured locking plates in a perpendicular configuration. Group 3 used precontoured locking plates in a parallel configuration. Each group was tested for stiffness in anterior bending, posterior bending, axial compression, and torsion. The specimens then underwent cyclic loading followed by single load to failure in posterior bending.Findings: There was no significant difference between the three groups for anterior bending, posterior bending, axial compression, or torsional stiffness. There was no significant difference in load to failure for any of the three groups. Screw loosening was significantly higher in Group 1 when compared to Groups 2 and 3 after cyclic loading.Interpretation: In the early postoperative period, less expensive perpendicular conventional reconstruction plate constructs provide similar stiffness and load to failure properties to newer precontoured locking plate systems regardless of plate configuration.

Does prior sustained compression make cartilage-on-bone more vulnerable to trauma? - Corrected Proof

Woong Kim, Ashvin Thambyah, Neil Broom — 2012-04-26

Abstract: Background: This study investigated how varying levels of prior creep deformation in cartilage-on-bone samples influences their mechanical response and vulnerability to structural damage following a single traumatic impact.Methods: Bovine patellae were subjected to varying intervals of prior creep loading at a constant stress of 4MPa. Immediately following removal of this stress the samples were impacted with a pendulum indenter system at a fixed energy of 2.2J.Findings: With increasing prior creep, the peak force on impact rose, the duration of impact and time to reach peak force both decreased, and both the energy dissipated during impact and the magnitude of impulse were both unchanged by the level of prior creep. With increasing prior creep, the severity of impact-induced osteochondral damage increased: articular cartilage cracks penetrated to a greater depth, extending to the calcified cartilage layer resulting in hairline fractures or articular cartilage delamination and associated secondary damage to the vascular channels in the subchondral bone.Interpretation: The study shows that exposure of the cartilage-on-bone system to prior creep can significantly influence its response to subsequent impact, namely force attenuation and severity of damage to the articular cartilage, calcified cartilage and vascular channel network in the subchondral bone.

How do elliptical machines differ from walking: A study of torso motion and muscle activity - Corrected Proof

Janice M. Moreside, Stuart M. McGill — 2012-04-25

Abstract: Background: The elliptical trainer is a popular exercise modality, yet its effect on the lumbar spine is poorly understood. The purpose of this study was to analyze the effect of different hand positions, speed and stride lengths on spine kinematics and corresponding muscle activity while using the elliptical trainer, and compare with those demonstrated in normal walking.Methods: Electromyographic data was collected over 16 trunk and gluteal muscle sites on 40 healthy males (mean age (SD)=23(3)) while on the elliptical trainer. Two stride lengths (46, 66cm), 2 speeds (self-selected, 30% faster), and 3 hand positions (freehand, central bar, handles) were analyzed. Lumbar spine kinematics was calculated from data collected using a motion capture system. Results were compared to those found in walking using repeated measures ANOVA for each dependent variable with Bonferroni adjustments (P<0.004. Correlations were made between lumbar motion and various anthropometric measures.Findings: All significance levels comparing walking to elliptical varied according to stride length, speed and hand position. Average lumbar flexion angles and lumbar rotation were generally greater on the elliptical trainer, whereas walking produced more frontal motion. Total lumbar flexion/extension was similar between the two activities. Muscle activation patterns of the gluteal muscles were consistently higher on the elliptical, whereas the back extensors, latissimi and internal obliques were greater in only selected conditions.Interpretation: The various hand positions, speeds and stride lengths affect lumbar motion and muscle activity on the elliptical trainer, thus must be considered when incorporated into an exercise protocol.

Functional electrical stimulation elliptical stepping versus cycling in spinal cord-injured individuals - Corrected Proof

Nur Azah Hamzaid, Karla R. Pithon, Richard M. Smith, Glen M. Davis — 2012-04-19

Abstract: Background: The cardiorespiratory responses and mechanical efficiencies of two modalities of functional electrical stimulation augmented leg exercises – isokinetic cycling and isokinetic elliptical stepping – were compared amongst individuals with spinal cord injury.Methods: Five subjects performed seated isokinetic evoked cycling and elliptical stepping leg exercise at 10, 20 and 30rev·min−1 pedal cadences. 3-D motion analysis and force transducers attached onto the foot pedals quantified the external forces and power outputs developed by each lower extremity. Hip, knee and ankle joints power were derived via inverse dynamics analysis. The subjects' cardiorespiratory responses during exercise were measured by respiratory gas analysis.Findings: Ensemble-averaged oxygen uptakes across pedal cadences were higher during stepping (448 (75) ml·min−1) compared to cycling (422 (54) ml·min−1). External power outputs and metabolic efficiencies during stepping (9.9 (8.3) W, 2.9 (3.2) %) were double those observed during cycling (5.3 (6.3) W, 1.6 (1.9) %). Cumulative internal and external leg joint powers during stepping were twice higher than cycling, but the stepping mechanical efficiencies derived from inverse dynamics analysis were comparable to cycling (76.3 (21.2) % and 63.6 (12.3) % respectively). Heart rate responses were similar between cycling and stepping, while carbon dioxide production and expired ventilation were slightly higher during elliptical stepping.Interpretation: Both exercise modalities could deliver appropriate training stimuli for improving the aerobic fitness and leg pedalling strength of spinal cord-injured individuals. However electrical stimulation-enhanced elliptical stepping might provide greater exercise dose-potency for leg muscle strengthening than electrically-enhanced cycling due to the higher power outputs observed.

The mechanical effect of the existing cement mantle on the in-cement femoral revision - Corrected Proof

2012-04-16

Abstract: Background: Cement-in-cement revision hip arthroplasty is an increasingly popular technique to replace a loose femoral stem which retains much of the original cement mantle. However, some concern exists regarding the retention of the existing fatigued and aged cement in such cement-in-cement revisions. This study investigates whether leaving an existing fatigued and aged cement mantle degrades the mechanical performance of a cement-in-cement revision construct.Methods: Primary cement mantles were formed by cementing a polished stem into sections of tubular steel. If in the test group, the mantle underwent conditioning in saline to simulate ageing and was subject to a fatigue of 1 million cycles. If in the control group no such conditioning or fatigue was carried out. The cement-in-cement procedure was then undertaken. Both groups underwent a fatigue of 1 million cycles subsequent to the revision procedure.Findings: Application of a Mann–Whitney test on the recorded subsidence (means: 0.51, 0.46, n=10+10, P=0.496) and inducible displacement (means: 0.38, 0.36, P=0.96) revealed that there was no statistical difference between the groups.Interpretation: This study represents further biomechanical investigation of the mechanical behaviour of cement-in-cement revision constructs. Results suggest that pre-revision fatigue and ageing of the cement may not be deleterious to the mechanical performance of the revision construct. Thus, this study provides biomechanical evidence to back-up recent successes with this useful revision technique.

Evaluation of femoral strains with cementless proximal-fill femoral implants of varied stem length - Corrected Proof

2012-04-16

Abstract: Background: The design intent of proximally-filling lateral flare femoral stems is to load the endosteal surface of the proximal femur both laterally and medially, to achieve normal bone strains. However, the long stem can contact the femoral cortex and may offload the proximal region to some extent. Therefore, in this study, we sought to determine if reducing the stem length, would result in physiologic strain patterns.Methods: Using the PhotoStress® method we analyzed 13 femurs intact and with three different stem length implants: stemless, ultra-short and short. The test rig loaded the femoral head by simulating the mid-stance single leg support phase of gait with the ilio-tibial band and the hip abductor forces. The strain distribution with each stem length implant was then compared to the intact strain distribution to determine which was most similar.Findings: As the stem length increased the femurs exhibited a typical pattern of reduced proximal strain and increased distal strain. However, there was some variation in this pattern indicating that the exact stem position and the location of its interaction with the endosteal surface of bone was not the same in each femur.Interpretation: The stemless design provided the best match compared to the native femur and therefore has the greatest potential to address the shortcomings of a stemmed femoral implant. However, the ultra-short implant also exhibited a strain distribution that closely emulated the intact femur, and may represent the best option as there are still several questions pertaining to stability and alignment of a stemless implant.

Impact of strut height on offloading capacity of removable cast walkers - Corrected Proof

Ryan T. Crews, Fraaz Sayeed, Bijan Najafi — 2012-04-05

Abstract: Background: Reducing weight-bearing stress to diabetic foot ulcers is critical to healing and commonly called offloading. Removable cast walkers are frequently used for offloading; however, patient compliance is often poor. Walkers commonly extend to the knee. Patients complain about walkers' weight and diminished balance with their use. This study compared the offloading capacity of walkers that varied by height. Heights included: knee, ankle, and shoe levels. To ensure a fair comparison the outsole and insole were standardized across the devices.Methods: Eleven diabetic subjects with moderate to high risk of ulceration were recruited. Subjects completed four 20m walking trials. Subjects performed one trial with each walker and one trial with an athletic shoe. Primary outcomes focused on plantar loading and were measured by pressure insoles. Secondary outcomes were associated with gait kinematics as collected by body worn sensors.Findings: Significant differences were found for the peak pressure and pressure time integrals of the different footwear. All walkers performed better than the athletic shoe. The ankle and knee-high devices performed best. Center of mass rotation data showed a trend of the ankle walker yielding a smaller range of motion (18% medial/lateral and 22% anterior/posterior) than the knee level.Interpretation: The ankle-high walker was able to provide similar offloading capacities as the knee-high walker. The diminished weight, along with potentially improved stability, may result in improved compliance with ankle-high walkers. A study comparing the use of the two devices for treating ulcers is now suggested.

Progressive hip rehabilitation: The effects of resistance band placement on gluteal activation during two common exercises - Corrected Proof

Edward D.J. Cambridge, Natalie Sidorkewicz, Dianne M. Ikeda, Stuart M. McGill — 2012-04-05

Abstract: Background: A critical issue for constructing a progressive rehabilitation program is the knowledge of muscle activation levels across exercises and within exercise modifications. Many exercises are offered to enhance gluteal muscle activation during functional rehabilitation but little data exists to guide the progression of exercise intensity during rehabilitation. The objective of this paper was to examine the effects of altering resistance band placement during ‘Monster Walks’ and ‘Sumo Walks.’Methods: Nine healthy male volunteers formed a convenience sample. Sixteen electromyography channels measured neural drive of selected muscles of the right hip and torso muscles. Three resistance band placements (around the knees, ankles and feet) during the two exercises were utilized to provide a progressive resistance to the gluteal muscles while repeated measures ANOVA with Bonferroni adjustment was used to assess differences in mean EMG. The presentation of exercises and band placement were randomized.Findings: Examining muscle activation profiles in the three hip muscles of interest revealed the progressive nature of the neural drive when altering band placement. Tensor fascia latae (TFL) demonstrated a progressive activation moving the band from the knee to the distal band placement, but not between the ankle and foot placements. Gluteus medius demonstrated a progressive activation moving distally between band placements. Gluteus maximus was preferentially activated only during the foot placement.Interpretation: The band placements offered a progressive increase in resistance for hip rehabilitation, specifically the gluteal muscles. The added benefit of placing the band around the forefoot was selective enhancement of the gluteal muscles versus TFL presumably by adding an external rotation effort to the hips. This information may assist those who address gluteal activation patterns for patients suffering hip and back conditions where gluteal activation has been affected.

Biomechanical evaluation of two intramedullary nailing techniques with different locking options in a three-part fracture proximal humerus model - Corrected Proof

2012-04-05

Abstract: Background: Osteosynthesis of unstable proximal humerus fractures still remains challenging. The aim of this study was to investigate two intramedullary nailing techniques with different locking options in a three-part fracture model and prove whether two new fixation concepts, introducing additional locking screw-in-screws inserted through the head of the proximal screws, and a calcar screw, provide better stability.Methods: A biomechanical testing model for three-part proximal humerus fractures including cyclic axial loading with increasing peak load and simultaneous pulling forces at the rotator cuff was used to test 12 pairs of human cadaver humeri, assigned to four groups and instrumented with either Targon PH (T1) or MultiLoc PHN in 3 different configurations (standard M1; two additional screw-in-screw M2; one additional calcar screw and two screw-in-screw M3).Findings: Initial range of motion in internal–external rotation and mediolateral translation was smallest in M3 (1.82°; 0.11mm), biggest in T1 (3.63°; 0.51mm) and significantly different between these two groups (p=0.02 and p=0.04, respectively). M3 showed minimum head migration along the nail and varus tilting after 5000 cycles (0.31mm; 0.20°) and 10000 cycles (1.59mm; 0.34°). M2 and M3 performed better than M1 and T1 regarding varus collapse. The highest number of cycles to failure was observed for M3 (20733) and the lowest for T1 (10083) with significant difference between these two groups (p=0.04).Interpretation: The configuration with two screw-in-screw and a calcar screw was superior in most aspects. The screw-in-screws were found to contribute against varus collapse. Both new fixation concepts could provide better stability in proximal humerus fractures.

The influence of bone cement type on production of fretting wear on the femoral stem surface: A preliminary study - Corrected Proof

H.Y. Zhang, L.A. Blunt, X.Q. Jiang, L.T. Fleming, S.M. Barrans — 2012-03-30

Abstract: Background: It has been reported that bone cement correlates with survivorship of cemented total hip replacement. However, little research has been published to investigate the influence of bone cement type on production of fretting wear on the femoral stem.Methods: In the present study, we performed six in vitro wear simulations using the same type of femoral stem (polished Exeter V40™) and three different bone cements (Simplex P, Palacos R, and CMW 3).Findings: Fretting wear was consistently reproduced on the stem surface and the wear locations compared well with the results of retrieval studies. Selected 3D surface parameters were utilised to quantitatively evaluate fretting wear and no significant difference was identified in terms of fretting wear severity between these simulations. The bone cements were all badly damaged in those sites contacting the fretting wear areas on the femoral stem. Additionally, there were plenty of wear debris present on the cement surface, and the energy dispersive X-ray analysis confirmed that it was just cement particles for Simplex P bone cement, whilst it included metallic particles for Palacos R and CMW 3 bone cements.Interpretation: This preliminary study shed some light on the influence of bone cement type on production of fretting wear on the femoral stem surface but further research is needed to gain a better understanding on this issue.

The relationship between rearfoot, tibial and hip kinematics in individuals with patellofemoral pain syndrome - Corrected Proof

2012-03-22

Abstract: Background: Excessive rearfoot eversion is thought to be a risk factor for patellofemoral pain syndrome development, based on theoretical rationale linking it to greater tibial internal rotation and hip adduction. This study aimed to establish the relationship of rearfoot eversion with tibial internal rotation and hip adduction during walking in individuals with and without patellofemoral pain syndrome.Methods: Twenty-six individuals with patellofemoral pain syndrome and 20 controls (18–35years) participated. Each underwent instrumented three-dimensional motion analysis during over-ground walking. Pearson's correlation coefficients (r) were calculated to establish the relationship of rearfoot eversion with tibial internal rotation and hip adduction (peak and range of motion).Findings: Greater peak rearfoot eversion was associated with greater peak tibial internal rotation in the patellofemoral pain syndrome group (r=0.394, P=0.046). Greater rearfoot eversion range of motion was associated with greater hip adduction range of motion in the patellofemoral pain syndrome (r=0.573, P=0.002) and control (r=0.460, P=0.041) groups; and greater peak hip adduction in the control group (r=0.477, P=0.033).Interpretation: Associations between greater rearfoot eversion and greater hip adduction indicate that interventions targeted at the foot or hip in individuals with patellofemoral pain syndrome may have similar overall effects on lower limb motion and clinical outcomes. The relationship between rearfoot eversion and tibial internal rotation identified in the patellofemoral pain syndrome group may be related to aetiology. However, additional prospective research is needed to confirm this.

Principal component based analysis of biomechanical inter-trial variability in individuals with chronic ankle instability - Corrected Proof

Kristof Kipp, Riann M. Palmieri-Smith — 2012-03-19

Abstract: Background: Biomechanical variability during movement may influence joint stability in individuals with chronic ankle instability (CAI). The purpose of this study was to compare the kinematic and the kinetic inter-trial variability between healthy and CAI individuals.Methods: Eleven individuals with CAI and 11 matched controls performed five repetitions of a single-leg landing task. Biomechanical data were collected from 100ms before to 200ms after touchdown, and were used to calculate touchdown angles, peak angles and moments at the ankle joint in the frontal and sagittal planes. In addition, principal component analyses were used to quantify kinematic and kinetic patterns in the same planes across the 300ms time window. Five trial averages and inter-trial variability were calculated for all variables for each subject. Independent t-tests were used to compare variables between groups.Findings: The CAI group displayed greater inter-trial variability for principal component scores in the sagittal and frontal planes. The sagittal plane principal component captured a phase shift in plantar–flexion motion before touchdown, while the frontal plane principal component captured the general magnitude of motion during the entire movement. The CAI group therefore exhibited greater inter-trial variability in the sagittal plane before touchdown and in the frontal plane during the entire movement.Interpretation: While average motions did not differ between groups, the CAI group displayed greater kinematic inter-trial variability when analyzed with the principal component analysis. More variable joint motions may indicate less dynamic stability in the CAI group, which may originate from greater ligamentous laxity or diminished neuromotor control.

Symmetry of foot alignment and ankle flexibility in paediatric Charcot–Marie–Tooth disease - Corrected Proof

2012-03-19

Abstract: Background: Charcot–Marie–Tooth disease is the most common inherited nerve disorder and typically presents with pes cavus foot deformity and ankle equinus during childhood. Level in the variation of symmetry of musculoskeletal lower limb involvement across the clinical population is unknown, despite early reports describing gross asymmetry.Methods: We measured foot alignment and ankle flexibility of the left and right limbs using accurate and reliable standardised paediatric outcome measures in 172 patients aged 3–20years with a variety of disease subtypes recruited from the United States, United Kingdom, Italy and Australia.Findings: While a large range of differences existed between left and right feet for a small proportion of children, there was no overall significant difference between limbs.Interpretation: There are two important implications of these findings. Children with Charcot–Marie–Tooth disease generally exhibit symmetrical foot alignment and ankle flexibility between limbs. As such, analysing one limb only for biomechanical-related research is appropriate and satisfies the independence requirements for statistical analysis. However, because there are large differences between feet for a small proportion of children, an individualised limb-focused approach to clinical care is required.

Differences in gait pattern parameters between medial and anterior knee pain in patients with osteoarthritis of the knee - Corrected Proof

2012-03-14

Abstract: Background: Patients with osteoarthritis of the knee have unique spatiotemporal gait alterations. These gait changes have not yet been differentiated according to the location of knee pain. The purpose of this study was to compare the gait patterns of patients with symptomatic knee osteoarthritis that exhibit either anterior or medial joint pain.Methods: 240 Patients with knee osteoarthritis were evaluated at one therapy center. Patients were divided into two groups according to the location of greatest pain in their worse knee. Patients underwent a computerized spatiotemporal gait analysis. Differences in gait patterns between the two knee pain locations were also examined within each gender.Findings: Compared with patients with pain in the anterior knee compartment, those with pain in the medial knee compartment exhibited a significantly slower walking speed (P<0.01), shorter step length (P<0.01), lower single-limb-support phase (P<0.01). These differences are witnessed mainly between the females in each group, whereas males differed only in single-limb-support.Interpretation: The results of this study suggested underlying gait differences in the nature of medial and anterior knee pain. Furthermore, gender differences in gait may exist between patients with medial knee pain compared to patients with anterior knee pain.

Kinematic and kinetic modifications in walking pattern of hip osteoarthritis patients induced by intra-articular injections of hyaluronic acid - Corrected Proof

2012-03-14

Abstract: Background: A growing body of evidence points to the efficacy of intra-articular injections of hyaluronic acid, in dealing with pain and function in hip osteoarthritis. To date, however, no data exist as to this treatment's effect on walking pattern.Methods: We performed a prospective, open study in order to verify, in a group of 20 hip osteoarthritis patients (12 men, 8 women, mean age 60.5, range 47–73), the clinical effects of 3 intra-articular injections of 2ml of hyaluronic acid in the hip (1/week) in terms of pain and function at 1 (T1), 3 (T2) and 6-month (T3) follow-ups, as well as changes in the kinematics and kinetics of gait at 6-month follow-up.Findings: Pain as measured with visual analog scale significantly dropped after this procedure (P<0.0001). A significant improvement was noted regarding stiffness (P=0.005) and disability (P=0.04), as measured by the Western Ontario and McMaster Universities osteoarthritis index. As regards gait analysis, patients at T3 walked with higher cadence (P=0.004) and stride length (P=0.02) compared to T0. Moreover, a significant increase for the pelvic tilt at heel contact (P=0.0004) and for hip flexion–extension moment at loading response sub-phases of gait cycle (P=0.02) was noted at T3.Interpretation: In line with current literature, our patients display clinical improvement 6months after intra-articular injections of hyaluronic acid, accompanied by changes in walking pattern, as measured by instrumental gait analysis. The kinematic and kinetic changes observed may be the consequence of the therapeutic effect of intra-articular injections of hyaluronic acid.

Kinematic covariation in pediatric, adult and elderly subjects: Is gait control influenced by age? - Corrected Proof

Corinne Bleyenheuft, Christine Detrembleur — 2012-03-05

Abstract: Background: In human walking, kinematics of lower limb segments covary. Our objective was to assess the impact of age at different speeds (slow, medium and fast) on kinematic segmental covariation in normal subjects.Methods: Thirty subjects ranged into 6 age groups (“5years”, “10years”, “15years”, “20years” and “70years”) were included. We performed a gait analysis on a treadmill at 3 predetermined speeds: 1 (slow), 3 (medium) and 5 (fast) kmh−1, except for the 5years group who was unable to walk at 5kmh−1. Kinematic segmental covariation was computed and represented by a 3D-loop, described by a principal component analysis (Borghese's methodology). We studied the percentage of variance of each component of the principal component analysis, knowing that the percentage of variance of the first and the second components reflected the shape of the loop, and that the percentage of variance of the third component was an index of its planarity. The effect of age was tested using a one-way analysis of variance.Findings: When comparing the age groups at the same speed, we found a significant difference in the percentage of variance of the first and the second components between the 5 and the 10years at 3kmh−1. We also noticed a difference in the percentage of variance of the third component at 5kmh−1 between the 10years and the 15 and 20years groups.Interpretation: We observed that kinematic covariation remains stable throughout adulthood between 15 and 70years old at slow, medium and fast speed. In children, a mature percentage of variance of the first and the second components is acquired from 10years old and a mature percentage of variance of the third component from 15years old.

The stabilizing role of the rotator cuff at the shoulder—responses to external perturbations - Corrected Proof

A. Day, N.F. Taylor, R.A. Green — 2012-03-05

Abstract: Background: The rotator cuff has been hypothesized as a dynamic stabilizer at the shoulder joint yet evidence supporting this role remains inconclusive. We aimed to investigate the activity levels and recruitment patterns between the rotator cuff and superficial shoulder muscles in response to external perturbations to provide insight into the stabilizing role of the rotator cuff.Methods: Surface and intramuscular electromyography (EMG) were used to measure timing of onset and level of activation (EMG amplitude as a percentage of maximum voluntary isometric contraction, % MVIC) of rotator cuff (supraspinatus, infraspinatus and subscapularis) and superficial muscles (anterior and posterior deltoid) on 19 healthy participants. Participants received expected and unexpected externally applied perturbations in directions of internal and external rotation at the glenohumeral joint.Findings: All three rotator cuff muscles demonstrated pre-activation in anticipation of the perturbation prior to their representative global synergists, anterior and posterior deltoid (P<0.05). Subscapularis and infraspinatus were activated prior to all other muscles during external rotation and internal rotation perturbation trials respectively (P<0.01). Direction specific activation levels were observed; subscapularis was moderately strongly active (37% MVIC) in response to an external rotation perturbation and infraspinatus was moderately active (28% MVIC) in response to an internal rotation perturbation. No muscle was activated >10% MVIC when not acting as the main muscle opposing the movement.Interpretation: The rotator cuff may function in part as a dynamic stabilizing unit of the shoulder demonstrating a feedforward muscle activation pattern. These results may assist in improving assessment and treatment of shoulder dysfunction.

Impact of ankle osteoarthritis on the energetics and mechanics of gait: The case of hemophilic arthropathy - Corrected Proof

2012-03-02

Abstract: Background: Osteoarthritis may affect joints in any part of the body, including the ankle. The purpose of this study was to assess the impact of ankle osteoarthritis on the energetics and mechanics of gait, while taking into account the effect of slower speed generally adopted by patients with osteoarthritis.Methods: Using a motion analysis system, synchronous kinematic, kinetics, spatiotemporal, mechanics and metabolic gait parameters were measured in 10 patients diagnosed with ankle osteoarthritis consecutive to hemophilia. The subjects walked at a self-selected speed and their performance was compared to speed-matched normal values obtained in healthy control subjects.Findings: Speed-normalization using a Z-score transformation showed a significant increase in metabolic cost (Z=1.78; P=0.006) and decrease in mechanical work (Z=−0.97; P=0.009). As a consequence, muscular efficiency also decreased (Z=−0.97; P=0.001). These changes were associated with a surprising efficacy of the pendular mechanism, i.e., an improved recovery index (Z=0.97; P=0.004).Interpretation: Our findings suggest that patients with ankle osteoarthritis adopt a walking strategy which improves recovery through the pendular mechanism. This may be a compensatory mechanism in order to economize energy which would counterbalance the energy waste due to low muscle efficiency. These modifications are proportional to the impaired ankle function. Our data provides a quantitative baseline to better understand the dynamics of ankle osteoarthritis and determine the individual role that lower limb joints play in the multiple chronic joint affections.

Distal femoral fixation: A biomechanical comparison of retrograde nail, retrograde intramedullary nail, and prototype locking retrograde nail - Corrected Proof

2012-02-27

Abstract: Background: Distal femur fractures continue to be a complex surgical problem for which the incidence is increasing. Presently, there is a need for different constructs to address these complex fractures. This study attempts to define the biomechanical properties of several implants.Methods: A novel, prototype locking retrograde intramedullary nail and the Russell–Taylor femoral retrograde nail were tested at non-destructive, physiological, axial mode load strength using a young, synthetic bone model for a medial segmental shaft defect in the supracondylar region of the distal femur (medial gap of 10mm, 65mm proximal to the distal joint and parallel to the knee axis). Each specimen was compressively loaded and unloaded to the peak load for 80,000cycles at a 0.5Hz frequency. These were compared to the results from the same lab of the retrograde Trigen intramedullary nail. Motion and peak displacement were measured across the fracture site as a reflection of construct stability.Findings: Previous testing demonstrated that Trigen intramedullary nail had significantly less motion across the gap and increased overall stiffness of the construct (P<0.05) compared to both Russell–Taylor and prototype nails.Interpretation: Locking technology used in a nail biomechanically appears to lead to more micro-motion across the fracture gap and to less stiffness in this construct. Further research needs to be invested into intramedullary, locking technology before introducing it into clinical practice.

Myometry revealed medication-induced decrease in resting skeletal muscle stiffness in Parkinson's disease patients - Corrected Proof

2012-02-27

Abstract: Background: Based on combined analysis of clinical assessment of parkinsonian rigidity (constant resistance force generated during passive movement in a joint), electromyography and/or dynamometry many studies showed objectively that anti-parkinsonian medication decreases the rigidity in Parkinson's disease (PD). Rigidity-related changes in resting muscle stiffness (changed muscle's mechanical property related to its structural changes and changed neural drive) in PD patients have been revealed by myometry, a simple, sensitive, and reliable method for measuring mechanical properties in human soft tissues.However, an application of myometry in estimation of medication effects on the PD rigidity-related muscle stiffness has not been reported yet. Therefore, our study aimed to assess medication-induced changes in resting muscle stiffness in PD patients using myometry.Methods: We measured resting muscle stiffness by myometry and recorded a surface electromyogram of relaxed biceps brachii, brachioradialis and triceps brachii muscles in ten patients with PD (age: 51–80years; Hoehn and Yahr stage: 2.5–4) during medication on-phase (when subjects felt best comfort and fitness after medication: Levodopa, Piribedil, Ropinirol) and medication off-phase (12h after withdrawal of the medication).Findings: Our patients had significantly lower myometric stiffness and electromyogram amplitude in all tested muscles, and also lower clinical rigidity scores during the medication on-phase compared with the medication off-phase.Interpretation: Myometry revealed that anti-parkinsonian medication decreases not only rigidity in PD, but also rigidity-related stiffness in resting skeletal muscles in PD patients. These findings show that myometry can enrich neurological practice, by allowing objective and reliable assessment of parkinsonian rigidity treatment effectiveness.

Gait analysis of adults with generalised joint hypermobility - Corrected Proof

2012-02-24

Abstract: Background: The majority of adults with Generalised Joint Hypermobility experience symptoms such as pain and joint instability, which is likely to influence their gait pattern. Accordingly, the purpose of the present project was to perform a biomechanical gait analysis on a group of patients with Generalised Joint Hypermobility and compare them to a group of healthy subjects.Methods: Seventeen adults clinically classified with Generalised Joint Hypermobility (6 males and 11 females) and seventeen healthy subjects (9 males and 8 females) were included in the project.The subjects walked across three force platforms while they were filmed by five video cameras. Net joint moments were calculated in 3D by inverse dynamics and peak values were input to statistical analyses. A 3D knee joint model was used to calculate bone-on-bone forces.Findings: In the frontal plane both the peak knee and hip abductor moments were 13% higher in the patient group. In the sagittal plane the peak knee extensor moment was 10% higher for the patients and the flexor moment about the knee joint in the middle of stance was 27% lower for the patients. Increased flexion in the knee joint for the patients was also observed.Interpretation: The finding that adults with Generalised Joint Hypermobility display higher joint moments during walking in both the frontal and the sagittal planes and increased knee joint loadings may explain the pain symptoms in the patient group and indicate these subjects are subjected to an increased risk of developing osteo-arthritis.

Knee rotational laxity: An investigation of bilateral asymmetry for comparison with the contralateral uninjured knee - Corrected Proof

A. Hemmerich, W. van der Merwe, M. Batterham, C.L. Vaughan — 2012-02-20

Abstract: Background: Instability associated with anterior cruciate ligament injury is commonly evaluated against the patient's contralateral knee. The objectives of this study were, therefore, to assess symmetry of rotational knee laxity in vivo under passive torsional loading in uninjured subjects, and to compare mean rotation of this control group with the contralateral, intact knees of anterior cruciate ligament deficient patients.Methods: Axial knee rotation was measured in 29 patients with unilateral anterior cruciate ligament injury and 15 uninjured age and gender-matched control subjects using an imaging-compatible torsional loading device. Side-to-side differences in internal, external, and range of knee rotation were assessed in the control group and mean bilateral knee rotation was compared to the patients' contralateral knee data at both full extension and 30° of flexion.Findings: Statistically significant differences in symmetry were found in three of the six measures of transverse plane rotation in the uninjured knees; a mean side-to-side difference of 2.2° in range of rotation was detected in the flexed position. No significant differences were observed between the mean values of the healthy control group and the contralateral knees of the anterior cruciate ligament deficient patients.Interpretation: Bilateral asymmetry of rotational laxity occurs in healthy individuals. Nevertheless, comparability of rotational knee laxity between the contralateral limbs of patients and the uninjured population was evidence that rotational laxity was not inherent or developed in the contralateral knees of the anterior cruciate ligament deficient participants.

Isokinetic knee extensor strength deficit following matrix-induced autologous chondrocyte implantation - Corrected Proof

Jay R. Ebert, David G. Lloyd, David J. Wood, Timothy R. Ackland — 2012-02-17

Abstract: Background: Autologous chondrocyte implantation has become an established technique for addressing knee cartilage defects. Despite reported improvement in pain and regeneration of hyaline-like repair tissue, little has been reported on the recovery of knee strength.Methods: Knee strength assessment was undertaken in 60 patients at 5years following autologous chondrocyte implantation. Using an isokinetic dynamometer, and during isokinetic knee extension and flexion angular velocities of 60°, 90° and 120°/s, the peak torque, torque at 45° of knee flexion and hamstrings/quadriceps ratio was obtained, in both the operated and non-operated limbs. Pain at the time of assessment was obtained. Independent sample t-tests were used to assess differences in the operated and non-operated sides.Findings: There were no significant differences (p>0.05) between the operated and non-operated legs in the peak knee flexor torque or knee flexor torque at a knee flexion angle of 45°, at all angular velocities (60°, 90° and 120°/s). While the peak knee extensor torque was less in the operated leg at all angular velocities, these differences were not significant (p>0.05). However, a significantly reduced (p<0.05) knee extensor torque at a knee flexion angle of 45°, was observed at all speeds.Interpretation: While patients had recovered their knee flexor strength, they still demonstrated a reduced knee extensor strength profile at 5years. This demonstrates that the early supervised rehabilitation phase following autologous chondrocyte implantation is not sufficient to restore long-term knee strength, and ongoing patient advice and rehabilitation is required extending beyond this early period. It is unknown how this prolonged reduction in strength may affect long-term graft outcome.

Corrective force analysis for scoliosis from implant rod deformation - Corrected Proof

Remel Salmingo, Shigeru Tadano, Kazuhiro Fujisaki, Yuichiro Abe, Manabu Ito — 2012-02-10

Abstract: Background: Scoliosis is a serious disease in which a human spine is abnormally deformed in three dimensions with vertebral rotation. Surgical treatment is attained when the scoliotic spine is corrected into its normal shape by implant rods and screws fixed into the vertebrae. The three-dimensional corrective forces acting at the screws deformed the implant rod during the surgical treatment of scoliosis. The objective of this study was to propose a method to analyze the three-dimensional forces acting at the rod using the changes of implant rod geometry before and after the surgical treatment.Methods: An inverse method based on Finite Element Analysis is proposed. The geometries of implant rod before and after the surgical treatment were measured three dimensionally. The implant rod before the surgical treatment was reconstructed using an elasto-plastic finite element model. The three-dimensional forces were applied iteratively to the rod through the screws such that the rod is deformed the same after the surgical treatment of scoliosis.Findings: The maximum force acting at the screw of each patient ranged from 198N to 439N. The magnitude of forces was clinically acceptable. The maximum forces occurred at the lowest fixation level of vertebra of each patient.Interpretation: The three-dimensional forces distribution that deformed the rod can be evaluated using the changes of implant geometry. Although the current clinical cases are still few, this study demonstrated the feasibility of measuring the forces that deformed the implant rod after the surgical treatment of scoliosis.

Gait termination strategies differ between those with and without ankle instability - Corrected Proof

Erik A. Wikstrom, Chris J. Hass — 2012-01-30

Abstract: Background: Chronic ankle instability is a common occurrence after an ankle sprain. Yet, some people (copers) possess a mechanism that limits recurrent injury and disability. During gait termination, those with chronic ankle instability exhibit altered feed-forward and feedback control but little is known about alterations in copers. Therefore, the purpose of this investigation was to determine the biomechanical control alterations present in controls, copers, and those with chronic ankle instability during planned and unplanned gait termination.Methods: Twenty subjects with chronic ankle instability, 20 copers, and 20 uninjured controls completed planned and unplanned gait termination tasks. Unplanned gait termination required subjects to stop, when cued, during randomly selected trials. Planned gait termination required intended stopping. A total of 10 trials were recorded for each condition. Normalized propulsive and braking force magnitudes and dynamic postural stability indices were calculated and compared among the groups.Findings: Normalized maximum braking forces were significantly higher in the chronic ankle instability group (Mean: 2.82 SD: 0.93N/kg), relative to copers (Mean: 2.59 SD: 0.84N/kg) and controls (Mean: 2.51 SD: 0.78N/kg). Similarly, the antero-posterior postural stability index revealed higher scores in the chronic ankle instability group (Mean: 0.15 SD: 0.03) compared to the coper (Mean: 0.14 SD: 0.02) and control group (Mean: 0.14 SD: 0.02). Copers did not differ from controls.Interpretation: The findings suggest that the ability of copers to terminate gait in a manner similar to uninjured controls may represent part of the underlying mechanism that limits recurrent injury and disability in copers.

A comparison of Anterior Cruciate Ligament graft tunnel orientation: Anatomic vs. transtibial - Corrected Proof

Michael S. Potter, Frederick W. Werner, Levi G. Sutton, Scott K. Schweizer — 2012-01-30

Abstract: Background: Recent Anterior Cruciate Ligament reconstruction techniques have emphasized reproducing the insertion sites of the native Anterior Cruciate Ligament. Anatomic techniques have shown improvements in biomechanical testing, but their superior results have not been shown clinically. The hypothesis of this study is that more oblique tunnels utilized in anatomic reconstructions cause asymmetric loading across the graft.Methods: Seven cadaver knees were tested in a knee simulator that performed a gait cycle and an anterior–posterior laxity test. Each knee underwent both reconstructions in random order utilizing the same Anterior Cruciate Ligament bone patellar tendon bone graft. Before reconstruction, the graft was split longitudinally and miniature force probes were inserted in the medial and lateral portions.Findings: During anterior–posterior laxity testing, the transtibial medial bundle averaged 74.8N compared to 87N for the anatomic. The lateral bundles averaged 146.2 and 158N respectively. Both reconstructions exhibited a similar ratio of force distribution between the bundles and there was no statistical difference. The average anterior–posterior motion for the intact knees was 10.8mm compared to 17.0mm after the Anterior Cruciate Ligament was sectioned. Anatomic reconstructions had an average of 14.0mm of laxity compared to 14.9mm for transtibial reconstructions (P<0.038).Interpretation: Greater obliquity did not lead to an increase in asymmetry of graft loading. The failure of anatomic reconstructions to show clinical improvement over transtibial reconstructions is not due to oblique tunnels causing asymmetric graft loading.

The biomechanical effects of a deepened articular cavity during dynamic motion of the wrist joint - Corrected Proof

Stefanie Erhart, Werner Schmoelz, Rohit Arora, Martin Lutz — 2012-01-30

Abstract: Background: A deepened articular cavity of the distal radius due to a metaphyseal comminution zone is associated with early osteoarthritis and reduced joint motion. As this deformity has not been investigated biomechanically, the purpose of this study was to evaluate the effects of a deepened articular cavity on contact biomechanics and motion range in a dynamic biomechanical setting.Methods: Six fresh frozen cadaver forearms were tested in a force controlled test bench during dynamic flexion and extension and intact mean contact pressure and contact area as well as range of motion were evaluated. Malunion was then simulated and intraarticular as well as motion data were obtained. Intact and malunion data were compared for the scaphoid and lunate facet and the total radial joint surface.Findings: Due to malunion simulation, cavity depth increased significantly. Motion decreased significantly to 54–69% when compared to the intact state. Malunion simulation led to a significant decrease of contact area in maximum extension for all locations (by ~50%). In maximum flexion and neutral position, contact area decrease was significant for the scaphoid fossa (by 51–54%) and the total radial joint surface (by 47–50%). Contact pressure showed a significant increase in maximum extension in the scaphoid fossa (by 129%).Interpretation: Already a small cavity increase led to significant alterations in contact biomechanics of the radiocarpal joint and to a significant range of motion decrease. This could be the biomechanical cause for degenerative changes after the investigated type of malunion. We think that restoration of the normal distal radius shape can minimize osteoarthritis risk post trauma and improve radiocarpal motion.

Predictive equations for lumbar spine loads in load-dependent asymmetric one- and two-handed lifting activities - Corrected Proof

N. Arjmand, A. Plamondon, A. Shirazi-Adl, M. Parnianpour, C. Larivière — 2012-01-20

Abstract: Background: Asymmetric lifting activities are associated with low back pain.Methods: A finite element biomechanical model is used to estimate spinal loads during one- and two-handed asymmetric static lifting activities. Model input variables are thorax flexion angle, load magnitude as well as load sagittal and lateral positions while response variables are L4–L5 and L5–S1 disc compression and shear forces. A number of levels are considered for each input variable and all their possible combinations are introduced into the model. Robust yet user-friendly predictive equations that relate model responses to its inputs are established.Findings: Predictive equations with adequate goodness-of-fit (R2 ranged from ~94% to 99%, P≤0.001) that relate spinal loads to task (input) variables are established. Contour plots are used to identify combinations of task variable levels that yield spine loads beyond the recommended limits. The effect of uncertainties in the measurements of asymmetry-related inputs on spinal loads is studied.Interpretation: A number of issues regarding the NIOSH asymmetry multiplier are discussed and it is concluded that this multiplier should depend on the trunk posture and be defined in terms of the load vertical and horizontal positions. Due to an imprecise adjustment of the handled load magnitude this multiplier inadequately controls the biomechanical loading of the spine. Ergonomists and bioengineers, faced with the dilemma of using either complex but more accurate models on one hand or less accurate but simple models on the other hand, have hereby easy-to-use predictive equations that quantify spinal loads under various occupational tasks.

Investigation into three dimensional hip anatomy in anterior dislocation after THA. Influence of the position of the hip rotation centre - Corrected Proof

Elhadi Sariali, Shahnez Klouche, Patrick Mamoudy — 2012-01-19

Abstract: Background: The components position is a major factor under the surgeon's control in determining the risk of dislocation post total hip arthroplasty. The aim of this study was to investigate the proper three-dimensional components position including the centre of rotation in the case of anterior dislocation.Methods: Among 1764 consecutive patients who underwent total hip arthroplasty using a direct anterior approach, 27 experienced anterior dislocation. The three-dimensional hip anatomy was investigated in 12 patients who were paired with 12 patients from the same initial cohort who did not experience dislocation and also with 36 control patients with osteoarthritis. A pelvic Cartesian referential was defined to perform the acetabular analysis. The coordinates were expressed as percentages of the pelvic width, height and depth. The anteversion angles were measured.Findings: The hip centre of rotation was significantly shifted medially and posteriorly in the dislocation group when compared to the non-dislocation group and also to the control group. There was no significant difference in component angular position between the dislocation-group and the non-dislocation group. However, the stem anteversion in the dislocation group was increased in comparison to the mean natural femoral anteversion of the control group.Interpretation: A medial and posterior displacement of the hip rotation centre was found to correlate to anterior dislocation post total hip arthoplasty. These results suggest the importance of an accurate restoration of the centre of rotation, whilst avoiding an excessive acetabular reaming which may induce a medial and a posterior displacement.Level of evidence: III comparative non randomised.

Gait patterns of asymmetric ankle osteoarthritis patients - Corrected Proof

2012-01-19

Abstract: Background: In early stages, ankle osteoarthritis is often asymmetric with only partially degenerated joint surfaces. There is only limited knowledge on the effect of asymmetric ankle osteoarthritis on the patients' gait patterns. Therefore, the aim of this study was to characterize kinematic and kinetic changes compared to healthy adults.Methods: Instrumented gait analysis was performed in eight asymmetric ankle osteoarthritis patients and 15 healthy controls. Beside conventional gait analysis methods, principal component analysis was used to analyze temporal progression of the most important variables: hindfoot dorsiflexion angle and vertical ground reaction force.Findings: Asymmetric ankle osteoarthritis patients had a lower hindfoot dorsiflexion and rotation range of motion as well as reduced peak ground reaction forces and peak kinetic values. Principal component analysis revealed that for both the hindfoot dorsiflexion angle and the vertical ground reaction force those principal component vectors affecting the amplitudes had significantly lower principal component scores in patients than in controls. The use of the principal component scores for classification with a linear support vector machine resulted in a high recognition rate of 97.8% for the discrimination between the affected leg and the healthy controls.Interpretation: Patients with asymmetric ankle osteoarthritis suffer from substantial pathological kinematic and kinetic gait changes. Principal component analysis combined with a linear support vector machine could successfully be used to temporally quantify and classify asymmetric ankle osteoarthritis gait patterns. This study therefore helps to understand the pathomechanism of early stage ankle osteoarthritis from a biomechanical view.

Alterations in in vivo knee joint kinematics following a femoral nerve branch block of the vastus medialis: Implications for patellofemoral pain syndrome - Corrected Proof

Frances T. Sheehan, Bhushan S. Borotikar, Abrahm J. Behnam, Katharine E. Alter — 2012-01-16

Abstract: Background: A potential source of patellofemoral pain, one of the most common problems of the knee, is believed to be altered patellofemoral kinematics due to a force imbalance around the knee. Although no definitive etiology for this imbalance has been found, a weak vastus medialis is considered a primary factor. Therefore, this study's purpose was to determine how the loss of vastus medialis obliquus force alters three-dimensional in vivo knee joint kinematics during a volitional extension task.Methods: Eighteen asymptomatic female subjects with no history of knee pain or pathology participated in this IRB approved study. Patellofemoral and tibiofemoral kinematics were derived from velocity data acquired using dynamic cine-phase contrast MRI. The same kinematics were then acquired immediately after administering a motor branch block to the vastus medialis obliquus using 3–5ml of 1% lidocaine. A repeated measures analysis of variance was used to test the null hypothesis that the post- and pre-injection kinematics were no different.Findings: The null hypothesis was rejected for patellofemoral lateral shift (P=0.003, max change=1.8mm, standard deviation=1.7mm), tibiofemoral lateral shift (P<0.001, max change=2.1mm, standard deviation=2.9mm), and tibiofemoral external rotation (P<0.001, max change=3.7°, standard deviation=4.4°).Interpretation: The loss of vastus medialis obliquus function produced kinematic changes that mirrored the axial plane kinematics seen in individuals with patellofemoral pain, but could not account for the full extent of these changes. Thus, vastus medialis weakness is likely a major factor in, but not the sole source of, altered patellofemoral kinematics in such individuals.

A comparative biomechanical study of a novel integrated plate spacer for stabilization of cervical spine: An in vitro human cadaveric model - Corrected Proof

Kamran Majid, Suresh Chinthakunta, Aditya Muzumdar, Saif Khalil — 2012-01-13

Abstract: Background: Integrated plate-spacer may provide adequate construct stability while potentially lowering operative time, decreasing complications, and providing less mechanical obstruction. The purpose of the current study was to compare the biomechanical stability of an anatomically profiled 2-screw integrated plate-spacer to a traditional spacer only and to a spacer and anterior cervical plate construct. In addition, the biomechanical stability of 2-screw integrated plate-spacer was compared to a commercially available 4-screw integrated plate-spacer.Methods: Two groups, each of nine cervical cadaver spines (C2–C7), were tested under pure moments of 1.5Nm. Range of motion was recorded at C5–C6 in all loading conditions (flexion, extension, lateral bending, and axial rotation) for the following constructs: 1) Intact; 2) 2-screw or 4-screw integrated plate-spacer; 3) spacer and anterior cervical plate; and 4) spacer only.Findings: All fusion constructs significantly reduced motion compared to the intact condition. Within the instrumented constructs, spacer and anterior cervical plate, 2-screw and 4-screw integrated plate-spacer resulted in reduced motion compared to the spacer only construct. No significant differences were found in motion between any of the instrumented conditions in any of the loading conditions.Interpretation: The application of integrated plate-spacer for anterior cervical discectomy and fusion is based on several factors including surgical ease-of-use, biomechanical characteristics, and surgeon preference. The study suggests that integrated plate-spacer provide biomechanical stability comparable to traditional spacer and plate constructs in the cervical spine. Clinical studies on integrated plate spacer devices are necessary to understand the performance of these devices in vivo.

Functional capacity, muscle strength and falls in women with fibromyalgia - Corrected Proof

2012-01-09

Abstract: Background: Patients with fibromyalgia have difficulty with activities of daily living, they exhibit reduced muscle strength and high incidence of reported falls. The objective of this study was to evaluate the functional performance and lower limb muscle strength in women with fibromyalgia and determine the relationship between muscle strength and falls.Methods: Sixteen females with fibromyalgia and 16 healthy women participated in the study. Pain intensity, fibromyalgia impact on quality of life, physical activity level and fall prevalence were assessed. The peak torque and the rate of torque development were determined in maximal voluntary isometric contraction (hip, knee and ankle joints) using a load cell. The 30s chair stand, 8ft up and go, sit and reach, and functional reach tests were used to characterize functional performance.Findings: Women with fibromyalgia showed deficits in lower limb muscle strength, balance and agility and exhibited decreased knee extension peak torque and rate of torque development. In addition, they showed lower hip adduction and extension peak torque in comparison to the control group (P>0.05). Hip extension rate of torque development, duration of fibromyalgia symptoms, overall pain, knee pain, and fibromyalgia impact were strong predictors of the number of falls in patients with fibromyalgia (R2=0.86; P<0.05), when considered collectively.Interpretation: Women with fibromyalgia showed reduced functional performance and lower limb muscle strength, mostly explained by pain. There was a high prevalence of falls in this population, as explained by hip extensors rate of torque development, duration of fibromyalgia symptoms and pain.

Changes in patellofemoral joint contact pressures caused by vastus medialis muscle weakness - Corrected Proof

Andrew Sawatsky, Doug Bourne, Monika Horisberger, Azim Jinha, Walter Herzog — 2012-01-09

Abstract: Background: Patellofemoral joint pain is a common knee disorder, but its underlying causes remain unknown. One proposed mechanism is an imbalance in force in the knee extensor muscles. Specifically, the vastus medialis and vastus lateralis are thought to play a crucial role in proper patellar tracking, and weakness in vastus medialis is thought to lead to a lateral shift in the patella causing increased contact pressures and pain. The purpose of this study was to create an animal model of vastus medialis weakness and to test the effect of this weakness on patellofemoral contact pressures.Methods: Experiments were performed using New Zealand white rabbits (mass 4.9–7.7kg, n=12). Loading of the patellofemoral joint was produced by femoral nerve stimulation of the knee extensor muscles. Knee extensor imbalance was produced by vastus medialis ablation. Fuji pressure sensitive film was used to record contact area, shape and pressures for maximal and sub-maximal, matched-force contractions at knee angles of 30°, 60°, and 90°.Findings: Patellofemoral peak pressures, average pressures, contact areas and contact shapes were the same across all loading conditions for matched-force contractions before and after elimination of vastus medialis.Interpretation: We conclude that vastus medialis weakness does not cause changes in patellofemoral contact pressures. Since the muscular and knee joint geometry in rabbits and humans is similar, we question the idea of vastus medialis weakness as a cause of patellar mal-tracking and patellofemoral joint pain.